Ligno-cellulose aggregate and blast cleaning process employing the same



Patented Dec. 16, 1952 LIGNO-CELLULOSE AGGREGATE AND BLAST CLEANINGPROCESS EMPLOYING THE SAME Joseph W. Ayers, Easton, Pa., assignor toAgrashell, Inc., a corporation of Delaware No Drawing.

Application March 1, 1948,

Serial No. 12,485

11 Claims. 1

This invention relates to processes for removing coatings and depositsfrom the surface of various materials and to improved so-calledsoft-grit impact cleaners for use in such processes. More specifically,it relates to the cleaning of metals and other relatively hardsubstances and involves the removal of incrustations thereon bybombardment or impingement of the surfaces thereof using various hard,dense, tough lignocellulose materials in particles of certain shape andsize.

Surfaces of stone, iron and the like are cleaned by bombardment withsand or other abrasives projected in a stream of compressed air or otherfluid, and although the cleaning is effectively accomplished, theabrasive qualities of the sand score, etch, and pit the surfaces treatedthereby limiting the field of utility of such processes. During WorldWar II, and since then, carbonencrusted surfaces of cylinders and otherengine parts, first soaked in solvents, have been cleaned by projectinga stream of compressed air containing cracked or ground walnut shells inthe form of angular particles against the surface of such parts. Thisblasting operation successfully cleans the metal surfaces withoutscoring or denting the same, but the abrasion and the impact of theangular particles is not sufficient to remove many deposits, whichcannot be conveniently softened with solvents, nor adequate toaccomplish the cleaning in as short a period of time as is desirable.

An object of the present invention is to provide an improved impactmaterial or aggregate capable of removing tenacious deposits orencrustations on metals and other materials without etching or indentingthe surface to be cleaned and capable of providing a sufficientlyforceful impact to accomplish the cleaning operation more effectively orin a shorter period of time than when the soft grit materials heretoforesuggested are used. Another object is to provide a process not requiringthe use of solvents.

The impact aggregate of the present invention may be described as beingcomposed of substantially spherical or rounded particles oflignc-cellulose materialsliaving densities of at name, the saidpaTrBEles-being of a size or sizes within the range of from 12 to 40mesh. The ligno-cellulose materials suitable include hard, dense, toughnut hells and seed stones or fruit pits, such as the she s of pecannuts, almond nuts, black walnuts, English walnut'sTapricotp its, peachpits and olive pitsjcocfinut shells, palm nut shells, and other suchmaterials having a hardness of at least 15 on the Vickers scale. Thematerials best suited for most cleaning operations have been determinedto be those having a distribution of particles throughout the range of14 to 30 mesh."

In preparing the aggregate of the present invention, the ligno-cellulosematerial is ground in such manner as to provide the particles in roundedshape, a suitable grinding apparatus and procedure being disclosed in myco-pending application Serial No. 683,226, filed July 12, 1946, and nowPatent No. 2,561,043 as of July 17, 1951. The ground product composedofthe round particles of widely varying sizes is classified or screenedto provide a out within the range of 12 to 40 mesh. Particles outside ofthis range either have decidedly less cleaning power or are actuallyinoperable when employed in air blasting.

In accordance with a limited embodiment of the invention, a superiorcleaning aggregate is obtained when both small and large particleswithin the range are present, each in a substantial amount. For example,in a product containing particles of from 14 to 30 mesh, most forcefulresults are ordinarily obtained when the aggregate is composedpredominantly of larger particles or those of 14 to 20 mesh, for exampleabout 54 per cent, by weight. In a 12 to 40 mesh product a major portionshould be between 12 and 18 mesh.

In the impact cleaning process using rounded particles, the action isneither a cutting, grinding nor abrading in the accepted meaning ofthese terms, but is essentially a pounding, battering, or bombarding bysuccessive impact of flying particles against the surface to which theblast is applied. The energy of each particle is small, but such energyis expended by the rounded particles upon an extremely small surfacearea. The cumulative effect of the thousands of particles successivelyhitting the same area loosens a surprisingly large number of hard,tenacious incrustations.

An outstanding advantage of the ligno-cellulose impact aggregates of thepresent invention is their resistance to fracture or disintegrationduring the cleaning operation. This toughness is of particularimportance in view of the economic necessity for reuse of the aggregatea number of times. The superior ligno-cellulose aggregates of theinvention, such as walnut shell particles and apricot pit particles canbe recycled through the blasting equipment approximately one hundredtimes before being reduced to ineffective sizes. In other words, thedust lost per cycle of use is approximately 1% of the weight of thecharge of the aggregate in the blasting equipment. By comparison sand isreduced to fines in only about five cycles.

As compared with the angular particles of ground walnut shellsheretofore suggested, the rounded particles of the same shells of thesame size show, on test, from four to eight times the cleaningefficiency. This means that through the use of the rounded particlesmore tenacious incrustations may be removed or that the same coatingsmay be removed more quickly and hence at less expense.

The process of the present invention using rounded ligno-celluloseparticles, which are nonabrasive, do not cause appreciable wear of thenozzles through which the particles are projected. In contrast theretoprocesses employing sand generally wear out the nozzles in as little asone week of normal or constant use.

The product and process of the present invention may be employed toclean a wide variety of materials including both hard and relativelysoft substances as iron, steel, brass, bronze and aluminum. The softermaterials, however, require gentler treatment than the harder ferrousmetals. The blasting of soft metals ordinarily may be satisfactorilyaccomplished by using lower pressures or lower particle velocity, oremploying particles of smaller diameter within thestated range, orselecting ligno-cellulose materials of lower specifie gravity, oremploying any combination of such procedures. If the surfaces of softmetals are to be cleaned without denting them, it is of course necessarythat a ligno-cellulose material be employed which has a hardness whichis not greater than the hardness of the surface to be cleaned.

Ordinarily, aluminum die castings can be cleaned sufficiently withoutdamage to the surface of the metal, but when aluminum sand castings areporous due to faulty production, the blasting process of the presentinvention will cause small air holes to appear in the casting. Thepresent process may also be employed to clean chrome plating on aluminumprovided the aluminum alloy under the plating is not too soft. Chromeplated steel surfaces may be speedily and efficiently cleaned.

One of the outstanding applications of the product and process of thepresent invention lies in the cleaning of tire. molds and other rubbermolds. Conventional methods for cleaning tire molds involving acetyleneburning and wire brush treatment have long been considered costly andtime consuming because of the danger from explosions and fires and thehand labor required. Such treatment, furthermore, plays havoc with moldsurfaces and it cannot be used at all on aluminum molds.

,The cleaning of such molds using the product of} the present inventionprovides speedy, economical and thorough cleaning without damaging themolds and without involving operating hazards. The small particles ofthe ligno-cellulose reach remote corners and crevices of the molds notaccessible by conventional cleaning methods. The blasting treatment notonly accomplishes cleaning, but also the surfaces are polished due tothe deposition of a thin coating of wax contained in the ligno-cellulosematerial. Such wax produces a protective coating and also avoids thenecessity of breaking in the molds after the cleaning has beenaccomplished. The cost of cleaning using the blasting process issubstantially less, or about one-third to one-ninth as much as theconventional process.

This cleaningprocess will also remove baked enamels from the surface ofglass, and paints from metal surfaces; synthetic resin flash from moldedparts containing metal units, particularly those used for electricalcircuits and connections, and for the peem'ng of washed metal surfacessuch as aluminum to increase their strength.

For the successful operation of the present invention, it is ordinarynecessary that high air pressures, long nozzles of relatively smalldiameter and well-cleaned, dust-free ligno-cellulose material beemployed. Conventional machines employing high pressure air may be usedin the practice of the invention and these may be either of the suctionfeed type or the direct pressure feed type. The latter type equipment isordinarily preferred, for it is capable of providing greater impact andhence superior cleaning results. The impact material may be used influid mediums other than air, as in water, steam, vapor or other liquidsor gaseous media.

When suction feed blasting equipment is employed, the aggregate iscontinuously recycled through such equipment without the necessity forrecharging until the particles are broken down. worn away or shatteredto fine dust. The nozzle used on this type of equipment is designed witha suction venturi which pumps the particles from the bottom of thecontainer holding them through a hose to the nozzle where they arepicked up by the air stream going through the nozzle against the surfacebeing blasted. They fall into a hopper below the apparatus from whichthey are again withdrawn by suction and recycled through the nozzle. Inthis type of equipment, a portion of the available kinetic energy isconsumed in recycling the particles through the system by the Venturiaction. A satisfactory nozzle is one of & inch size having a 3 inchlength providing a jet of A; inch size. In operating the processusingsuch nozzle an air pressure of approximately pounds per square inchis required.

When the present process is employed using direct pressure, theequipment includes a generator or pressure tank into which the aggregateis charged, and air pressure is applied to such tank in such manner asto force the particles into a mixing chamber. Beneath the tank an airstream picks up the particles as they leave the mixing chamber andcarries them through the hose leading to the blasting nozzle from whichthey are expelled at high velocity.

In operation the amount of the ground material must be carefullycontrolled in relation to the air stream leaving the nozzle. If theamount of ground material carried by the air stream is too great, thevelocity of the particles decreases and the blasting efiiciency dropsoff sharply. This direct pressure type equipment should likewise besupplemented by some means ofconveying the used particles whichaccumulate in the hopper below the blasting equipment back to thegenerator or pressure tank. This may be easily accomplished by means ofa screw conveyor and bucket elevator, or by airveying with a suctionsystem, or the particles may be transferred by hand.

With direct pressure equipment a nozzle of three to five inches lengthmay be employed hav-' ing a diameter of /2 inch or inch size. When suchnozzle is used, an air pressure of 90 pounds per square inch minimum inthe pressure tank should be employed.

In a series of commercial tests made on the cleaning of 600 x 16 sizecast steel rubber tire molds it was found that the time required toclean one mold with rounded particles of ligno-cellulose aggregates of14 to 30 mesh size was from 7 to 8 minutes. When ligno-celluloseaggregates of the same size and made from the same raw material, butground to an angular shape, were used, the time required for cleaningone mold ranged from 30 to 45 minutes.

Example In the table below a comparison is made of the breakdowntendencies of apricot pit aggregate composed of particles of roundconfiguration with an aggregate composed of particles of apricot pits ofangular configuration, the particles in both instances being of the samesize, that is a cut between and mesh. The operation was carried out in asuction feed blasting equipment in which the aggregates were projectedthrough a inch jet and a /2 inch nozzle for three minutes of continuousblasting, the amount of pressure being from 90 to 100 pounds.

The data in the above table shows that angular particles break downfaster to finer sizes in the same length of time of blasting. In otherwords, the angular particles wear out faster than rounded ones.

It should be understood that the present invention is not limited to thespecific materials or procedures hereinbefore described, but that itextends to all equivalents which will occur to those skilled in the artupon consideration of the scope of the claims appended hereto.

I claim:

1. An impact cleaner for use in blasting to remove coatings on metalsand other surfaces comprising an aggregate composed of rounded particlesof ligno-cellulose material having a density of at least 1.20, the saidparticles being of a size within the range of from 12 to mesh.

2. An impact cleaner for use in blasting to remove coatings on metalsand other surfaces comprising an aggregate composed of rounded particlesof ligno-cellulose material having a density of at least 1.20, the saidparticles being of mixed sizes of 12-40 mesh, a substantial proportionof which is between 12 and 18 mesh and another substantial proportion ofwhich is between 18 and 40 mesh.

3. An impact cleaner for use in blasting to remove coatings on metalsand other surfaces comrising an aggregate composed of rounded particlesof ligno-cellulose material having a density of at least 1.20, the saidparticles being between about 12 to 40 mesh size and predominantly of 12to 18 mesh size.

4. An impact cleaner for use in blasting to remove coatings on metalsand other surfaces comprising an aggregate composed of rounded particlesof hard, dense, tough, nut shells of a hardness of at least 15 and insizes Within the range of 12 to 40 mesh.

5. An impact cleaner for use in blasting to remove coatings on metalsand other surfaces comprising an aggregate composed of rounded particlesof walnut shells in sizes within the range of 12 to 40 mesh.

6. An impact cleaner for use in blasting to remove coatings on metalsand other surfaces comprising an aggregate composed of rounded particlesof fruit pit shells in sizes within the range of 12 to 40 mesh.

7. An impact cleaner for use in blasting to remove coatings on metalsand other surfaces comprising an aggregate composed of rounded particlesof apricot pit shells in sizes within the range of 12 to 40 mesh.

8. A process for removing coatings and deposits from surfaces of metalsand other materials which comprises bombarding the same with anaggregate composed of rounded parti cles of a ligno-cellulose materialhaving a density of at least 1.20, the said particles being of a sizewithin the range of from 12 to 40 mesh.

9. A process for removing coatings and deposits from surfaces of metalsand other mate rials which comprises directing against the same a highvelocity fluid stream containing an aggreate composed of roundedparticles of a hard. dense, tough, ligno-cellulose material of ahardness of at least 15 and of varying sizes within the ranges of from12 to 40 mesh.

10. A process for removing coatings and deposits from surfaces of metalsand other materials which comprises bombarding the same with a highvelocity compressed fluid stream containing an aggregate composed ofrounded particles of a ligno-cellulose material having a density of atleast.1.20, said particles being of mixed sizes of 12-40 mesh asubstantial proportion of which is between 12 and 18 mesh and anothersubstantial proportion of which is between 18 and 40 mesh.

11. A process for removing coatings and deposits from surfaces of metalsand other materials which comprises bombarding the same with a highvelocity compressed fluid stream containing an aggregate composed ofrounded particles of a ligno-cellulose material having a density of atleast 1.20, said particles being of about 14 to 30 mesh andpredominantly of 14 to 20 mesh.

JOSEPH W. AYERS.

REFERENCES (JITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,116,776 Wilcox Nov. 10, 19141,588,768 Moulton June 15, 1926 1,907,411 Timoney May 2, 1933 2,185,262Lupo, Jr Jan. 2, 1940 2,359,323 Lupo, Jr Oct. 3, 1944 2,421,806 PerryJune 10, 1947 2,462,982 MacClean Mar. 1, 1949

10. A PROCESS FOR REMOVING COATINGS AND DEPOSITS FROM SURFACES OF METALSAND OTHER MATERIALS WHICH COMPRISES BOMBARDING THE SAME WITH A HIGHVELOCITY COMPRESSED FLUID STRAM CONTAINING AN AGGREGATE COMPOSED OFROUNDED PARTICLES OF A LIGNO-CELLULOSE MATERIAL HAVING A DENSITY OF ATLEAST 1.20, AND PARTICLES BEING OF MIXED SIZES OF 12-40 MESH ASUBSTANTIAL PROPORTION OF WHICH IS BETWEEN 12 AND 18 MESH AND ANOTHERSUBSTANTIAL PROPORTION OF WHICH IS BETWEEN 18 AND 40 MESH.